1. Field of the Invention
The present invention relates to a roller spacing device to separate rollers by a constant distance so as to keep the rollers from touching each other. In particular, the roller spacing device is used in an image forming system having roller mechanisms which rotate in close contact under a given magnitude of pressure in an operating relationship between a photosensitive medium and a developing roller, between a photosensitive medium and a transferring roller, or between a photosensitive medium and a charging roller, and functions to separate the rollers by a constant distance so as to keep the rollers from touching each other when roller mechanisms are not used for a period of time.
2. Description of the Related Art
In a roller mechanism, more particularly, a roller mechanism having first and second roller members in close contact and rotating under a given pressure, each of the roller members is kept in contact under a given pressure regardless of their operation. Therefore, if at least one of the roller members is made of an elastic material such as rubber, leaving the roller members in contact under a pressure for a period of time may cause a permanent compressive deformation to the elastic roller member and distort its profile, so that the roller members may fail to achieve a desired effect.
In particular, in the case of a developing roller, a transferring roller or a charging roller provided in an electrophotographic image forming system, each roller is rotated in contact with an OPC drum as a photosensitive medium under a certain pressure. These rollers are also made of elastic rubber due to their properties. Therefore, when the image forming system is stored for a long time without being used, the rollers are subjected to profile distortion owing to the above-mentioned permanent compressive deformation, thereby having a fatal influence on an image. In addition, a low molecular organic substance which is a component of the developing, transferring and charging rollers may ooze onto the roller surface and mix with a developing agent so that a defective image may be generated.
An electrophotographic image forming system having such a roller mechanism will be described below with reference to FIGS. 1 and 2.
Referring to FIG. 1, the reference numeral 10 is an OPC drum functioning as a photosensitive medium, 20 is a charging device, 30 is a light exposure device, 40 is a developing device, 50 is a transferring device, 60 is a fusing device, 70 is a sheet feeder, and 80 is a body frame.
In this general electrophotographic image forming system, when a printing signal is inputted, discharge of the charging device 20 electrically and uniformly charges the surface of the OPC drum 10. The light exposure device 30 transforms an image signal from a computer or a scanner into a light signal, which is scanned into the OPC drum. This forms an electrostatic latent image in the OPC drum 10 in response to the image signal. Thereafter, the developing device 40 attaches toner to the area of the electrostatic latent image of the OPC drum so that the electrostatic latent image develops into a visible image with toner. When a printing sheet P fed from the sheet feeder 70 enters the transferring device 50, the toner image of the OPC drum 10 is transferred to the printing sheet P under a high voltage applied to the transferring device 50. The toner image transferred onto the printing sheet P is fused on the printing sheet P under heat and pressure while passing through a fusing device 60, and then the printing sheet P is discharged out of the system by a sheet discharging roller 90.
As shown in FIG. 2, the developing device 40 includes a toner vessel 41, a developing roller 42, a toner feed roller 43 and a constraint blade 44. Toner is fed onto the developing roller 42 by the toner feed roller 43, and then as the developing roller 42 rotates, the toner is transported into a developing nip N formed under contact between the developing roller 42 and the OPC drum 10. Here, toner is maintained in the form of a layer having a uniform thickness on the developing roller 42 by the constraint blade 44 which is fitted on the upper portion of the developing roller 42, and the toner layer is attached to the area of the electrostatic latent image of the OPC drum 10 so that the visible toner image is formed on the OPC drum 10.
Meanwhile, the developing device 40 is designed to apply a given pressure to its opposite ends so as to form the developing nip N between the developing roller 42 and the OPC drum 42 so that the OPC drum 10 contacts the developing roller 42 under a given magnitude of pressure. Accordingly, the developing roller 42 is generally made of an elastic rubber roller.
In the developing device 40 operated in such a contact developing way, as shown in FIG. 2, the OPC drum 10 and the developing roller 42 rotate in an opposite direction with respect to each other, maintaining the given developing nip N. The developing nip N is determined by pressure applied to the opposite ends of the developing device 40 including the developing roller 42. Until the developing device is delivered to a consumer after assembly, inspection and packing in a corresponding production line, the OPC drum 10 and the developing device 42 are in contact with a certain amount of pressure in their non-operative conditions.
The developing device described above is assembled in the production line and takes a long time until it is transferred to a common consumer. In particular, in a long distance export, the developing device takes a considerable time since it passes along various logistic systems. Therefore, if the developing device is stored without use for a long period of time, the developing roller 42, made of elastic rubber, is subjected to permanent compressive deformation at the developing nip N, resulting in roller profile distortion. In this way, such roller profile distortion deteriorates image quality, e.g., causing at least one horizontal band to be formed in the image. In particular, if the developing device is kept at a high temperature for a long time, the developing nip is under both heat and pressure. Then, a high viscous low molecular organic substance, that is a component in the developing roller, is extruded from the surface of the developing roller to mingle with the toner on the developing roller to form at least one horizontal band on the image, resulting in defective images. Accordingly, the above problems need to be improved.
Furthermore, the transferring roller and the charging roller constructed in the transferring device 50 and the charging device 20 in the general image forming system also come into contact with the OPC drum 10 in the same way as the developing roller 42. Therefore, the transferring roller or the charging roller tends to have the same problems as the developing roller.